The invention relates to an accumulator device for tying wire in a tying machine, particularly for pulp production, with an inlet to the accumulator device and an outlet from the accumulator device, and with a drive for tying wire.
In addition, the invention relates to a process for feeding the tying wire through an accumulator device to a tying device, particularly for pulp production, where the tying wire is fed through an inlet into the accumulator device and through an outlet out of the accumulator device to the tying device.
Tying machines are used in bale finishing lines in pulp production. Here, pulp bales (wrapped in pulp wrapping sheets or without wrapping), pulp stacks (3-4 bales with a total weight of approximately 1 metric tonne) or pulp units (2 stacks) are tied together with galvanized steel wire. Whenever bales are mentioned below, this can either mean pulp bales, pulp stacks or pulp units. The function of the tying machine is to transport a bale into the machine, apply up to nine steel wires per bale, and transfer the bale to the subsequent conveying device. The tying process involves winding the wire round the bale, drawing the wire taut, knotting the wire, and cutting the wire off the wire roll.
There are plants where the tying wire is pulled off a roll, threaded through an accumulator device, and then fed to a tying frame in which the pulp bales are tied up as described above. When it is wound round the bale, the wire is threaded around the bale in a tying frame. The wire loop closes in a tying head, containing a so-called twister, a gripper, and a cutter unit. Here the wire end that is still attached to the wire coming from the roll comes to rest on top of the leading wire end. As the wire is drawn taut, the wire end is clamped firmly in the gripper and the loop is pulled tight around the bale. The two wire ends are then twisted in the twister and the wire end is cut off from the rest of the wire.
A device of this kind is known from WO 01/68450 A2. In this device, the wire coming from the roll is fed through an accumulator drum to the tying frame. When the wire is drawn taut, the wire running into the accumulator drum is axial direction is wound round the accumulator drum. Here, the wire is wound round its own axis. Due to the very short cycle times, the wire forward feed speeds are currently up to 200 m/min., which results in consideration wear on the wire guides. If the wire is now also wound round its own axis, this leads to lateral displacement, which increases wear further. Moreover, the wire must have a relatively large diameter, currently around 3 mm, in order to provide the necessary stiffness required for the wire to be pushed easily through the guiding devices. A machine for tying up packages is known from EP 0 129 117 A1, using plastic tapes with little stiffness that have to be drawn round the package. U.S. Pat. No. 3,946,921 describes an accumulator for packing machines that also uses plastic tapes. In addition, DE 102 07 646 A1 shows temporary accumulator for a tying tape, i.e. also a material with little stiffness. The problems and solutions present here cannot be transposed to stiff tying wire.
A further problem is caused by the relatively high dynamic forces generated at high forward feed speeds of up to 200 m/min. when the wire or the drum on which it is wound is accelerated and braked.